The purpose of this work is to investigate the formation and release of prostaglandins in human platelets. We propose to determine the kinds and amounts of prostaglandins produced by platelets from normal human adults. We will investigate the agents that trigger, modify and inhibit the production of platelet prostaglandins. This study includes the characterization of the phospholipase A and the prostaglandin synthetase enzyme system of human platelets. Special attention will be paid to the effects of anti-inflammatory agents such as aspirin and indomethacin which are known to inhibit both prostaglandin formation and platelet aggregation to see whether there is a relationship between these phenomena. Finally, we shall search for abnormal phospholipase A activity or prostaglandins synthesized and released in the platelets of selected patients. The methods employed include tests of platelet aggregation, the release reaction, determinations of phospholipase A and qualitative and quantitative determinations of prostaglandins by bioassay, thin layer chromatography and gas chromatography.